1. Field of the Invention
The present invention generally relates to CMOS current steering circuits.
2. State of the Art:
It is well known to use current steering circuits for supplying and selectively directing current quantities to one or more outputs. Typically, a current steering circuit has a first stage for supplying a constant current, and a second stage--usually comprising two transistors in parallel--for steering the constant current. In operation of such current steering circuits, a pre-determined bias is applied to one of the transistors and the conductivity of the other transistor is controlled so that current is steered (i.e., routed) through the transistor that exhibits the highest conductivity. In conventional current steering circuits, regardless of where the second stage routes the current, the current drawn by the circuit is substantially constant.
Current steering circuits, as implemented in CMOS technology, are often designed for use in battery-operated applications. For example, such circuits are often used in battery-operated laptop computers. Because such current steering circuits have the above-mentioned characteristic of drawing the same quantity of current whether or not the current is needed by the applications hardware, the circuits unnecessarily reduce the operative time of the batteries.